1. Field of the Invention
The present invention relates to an automatic brake system and a method of controlling the same, and more specifically to a system for automatically braking an automotive vehicle for the prevention of a collision against another vehicle traveling ahead and a method of controlling the brake system automatically on the basis of both pump pressure and accumulator pressure.
2. Description of the Prior Art
As one of the recent safety countermeasures for an automotive vehicle, there has been proposed an automatic brake system such that the vehicle can be braked automatically in case a collision against an opposing object is predicted during travel. In general the brake system includes a pressure source composed of a pump driven by a motor to pump up a hydraulic medium (e.g., oil) and an accumulator for accumulating pressure generated by the pump in the ordinary brake system provided with an automatic brake system, an ABS (anti-lock braking system), a TCS (traction control system), etc. The pressure accumulated by the accumulator is introduced intermittently into the brake system through a solenoid valve in order to improve the pressure response to the braking system.
In the automatic brake system, however, the vehicle must be braked automatically over a wide speed range from a low speed of travel to a high speed of travel. Therefore, where the brake system is actuated on the basis of only the accumulator pressure in order to improve only the response characteristics to the braking system, various problems arises as follows: since the accumulator pressure is controlled by a solenoid valve, excessive surge pressure is inevitably generated whenever the solenoid valve is opened or closed momentarily and therefore the hydraulic pressure changes stepwise, with the result that the driving comfortability is deteriorated markedly in particular at low travel speed. On the other hand, when the brake system is actuated on the basis of only the pump pressure, the surge pressure can be reduced and therefore the hydraulic pressure can be controlled smoothly. However, the response characteristics of the pump pressure with respect to the brake system is not satisfactory, so that it is rather difficult to apply an emergency brake to the vehicle running at medium or high speed.
An example of the prior art automatic braking system is disclosed in Japanese Utility Model Laid-Open Application No. 63-24078. In this prior art reference, a hydraulic pressure generated by a hydraulic pressure source is accumulated in an accumulator, and the accumulated hydraulic pressure is supplied to wheel cylinders to actuate actuators in response to a control signal, in case there exists a danger of collision against an opposing object.
In the above-mentioned automatic brake system, however, since the brake system is actuated on the basis of only the accumulator pressure, the following problem arises: when the hydraulic pressure is set so as to be suitable for the emergency brake required when the vehicle is traveling at medium or high speed, it is difficult to brake the vehicle gently when the vehicle is traveling at low speed, so that the riding comfortability is deteriorated and further an excessive brake often causes a danger.